Alzheimer's disease is a devastating neurological disease characterized by extracellular deposits of amyloidbeta- peptides(Ab) and neurofibrillary tangles in the brains of patients. Genetic, pathological and biochemical evidence clearly support a causal link between Ab aggregates and Alzheimer's disease (AD) progression. Recent experiments strongly suggest that the toxicity of Ab may lie in the soluble oligomeric intermediates also called Ab-derived diffusible ligands (ADDL). The prediction of these studies is that either inhibiting the formation or disrupting the oligomerization of intermediates would be of therapeutic benefit in AD. We have recently established a novel dual selection strategy relying on phage-display that selects for beta-sheet presenting proteins that retain their original structure and evolve new functions, such as Ab binding. Our method has yielded an exciting set of proteins with preorganized beta-sheet epitopes that can interact differentially with Ab, where some soluble proteins strongly inhibit Ab fibril formation whereas other proteins strongly accelerate Ab fibril formation. In this proposal we seek to rigorously establish the mechanism of action of our amyloid-binding proteins (called hTB1 variants) and their effect upon Ab derived cellular toxicity. We propose to (1) characterize ten hTB1 variants selected against Ab for their ability to alter Ab fibrillization rates and also directly measure their binding to Ab fibrils; (2) characterize the binding of the hTB1 variants to intermediates along early and late stages of the Ab fibrillization pathway utlizing chemical crosslinking, sedimentation velocity and dynamic light scattering and finally (3) characterize the effect of the hTB1 variants upon the cellular neurotoxicity mediated by Ab. The ultimate objective is to correlate the various physical, kinetic and lexicological parameters obtained in these experiments to propose rational strategies for treating AD.